New chemical approaches involving polyfunctionalized C-ribosyl derivatives are used as versatile intermediates for the synthesis of new classes of C-nucleosides. Additionally, conversion of commercially available, as well as synthetic C-nucleosides, are used to obtain new analogs. The classes of synthetic C-nucleosides selected are isosteric with nucleosides of the nucleic acids and/or of the naturally occurring "purine-like" C-nucleoside antibiotics. Included in these classes are ribo-, 2-deoxyribo- and arabino-C-nucleoside derivatives of pyrimidines, pyrazoles, pyrazolo-triazines, pyrrolo-pyrimidines, thieno pyrimidines and pyridino-pyrimidines. The rationale for this study is based on (a) the demonstrated anticancer activities of closely related synthetic C-nucleosides prepared in our laboratories, and (b) on biochemical considerations. Ongoing biochemical and biological collaborative studies with several groups in this Institute provide the means for proper evaluation of these compounds and for uncovering any possible relationship between their structure and biological activity.